Name: _____________________________________
Date: ____________________
Activity 1.2.5 Clock Signals Using the 555 Timer
Introduction
The 555 Timer oscillator is one of the most common circuits used in introductory
electronics. It is a favorite among beginners because of its low cost and ease of
design. These are precisely the same reasons the 555 Timer is used in the Board
Game Counter design.
In this activity you will simulate and build a 555 Timer oscillator. You will observe the
effect that varying the value of its resistor and capacitor values has on the oscillation
frequency and duty cycle.
Equipment



Paper & pencil
Circuit Design Software (CDS)
Digital Logic Board (DLB)
Procedure
1. For the 555 Timer oscillator circuit shown below, calculate the frequency and
duty cycle of the output signal based on the component values shown.
2. Use the CDS to enter and simulate the 555 Timer oscillator circuit. Use the
oscilloscope’s markers to make the necessary measurements. Determine the
frequency and duty cycle of the output signal.
How do these values compare to the calculated values?
3. Repeat steps (1) and (2) for each set of component values in the table shown
below. Note that the shaded areas are the values that were measured from the
original circuit.
RA
RB
C
100 
330 
22 f
330 
330 
22 f
560 
330 
22 f
330 
100 
22 f
330 
330 
22 f
330 
560 
22 f
330 
330 
10 f
330 
330 
22 f
330 
330 
47 f
Period(T)
Frequency(f)
tH
tL
Duty
Cycle
Conclusion
1. Review the results of the data collected in step (3) of the procedure.

What effect did varying the RA have on the frequency and duty cycle?

What effect did varying the RB have on the frequency and duty cycle?

What effect did varying the C2 have on the frequency and duty cycle?